A flexible display device is useful and convenient. The flexible display device generally includes a flexible substrate and a display element layer formed on the flexible substrate. A method for making the flexible display device generally includes the following steps: forming a flexible substrate (e.g. polyimide substrate) on a hard support (e.g. glass support); then forming a display element layer on the flexible substrate; and finally removing the hard support. The hard support is configured to support the flexible substrate and the display element layer only during the process of making the flexible substrate. It is important to peel off the flexible substrate from the hard support completely.